Field of the Invention
The present invention relates to an electrolyte composition for a lithium-ion battery with at least one cathode and at least one anode, a lithium-ion battery containing the electrolyte composition, and also the use of a fluorine-containing carbonate component and lithium nitrate for, for example, improving the cycle stability and/or for increasing the performance of a lithium-ion battery.
Description of the Background Art
Anodes known in the prior art for lithium-ion batteries (LIB) are generally made of graphitic carbon, which provides a theoretical capacity of 372 mAh/g. A lithium metal oxide compound, such as lithium cobalt dioxide LiCoO2, lithium nickel dioxide LiNiO2, lithium manganese dioxide LiMnO2, lithium manganese oxide LiMn2O4, lithium nickel manganese oxide Li1.0Ni0.5Mn1.5O4, lithium nickel manganese cobalt oxide LiNi0.33Mn0.33Co0.33O2, or high energy lithium nickel manganese cobalt oxide Li1.2Ni0.176Mn0.524Co0.100O2, is normally used as the active material for the cathode. The two electrodes, which is to say the anode and the cathode, are connected to one another by a nonaqueous liquid electrolyte, a polymer electrolyte, or a gel electrolyte.
The nonaqueous liquid electrolytes generally have one or more organic solvents and a lithium salt dissolved therein. Examples of the lithium salts involved are lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), and lithium bis(oxalato)borate (LiBOB). The organic solvents typically are a combination of the following solvents: propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), tetrahydrofuran (THF), 1,2-dimethoxyethane (DME), and 2-methyltetrahydrofuran (2Me-THF).
US 2012/0129054 A1 discloses a silicon anode battery having an electrolyte composition that includes fluoroethylene carbonate, also called FEC, as one additive among others.
Aurbach et al. (Langmuir, 2012, 28, 6175 to 6184) succeeded in demonstrating that the addition of lithium nitrate LiNO3 to an electrolyte that has lithium bis(trifluoromethanesulfonyl)imide as conducting salt and dioxolane as solvent results in increased performance of lithium-ion batteries with silicon nanowires being used as the anode material.
Both the electrode materials and the electrolyte compositions can be changed or adjusted in order to increase the energy density for lithium-ion batteries. One possibility for improving the specific anode capacity is the use of elements that can enter into compounds with lithium, such as silicon, tin, antimony, aluminum, magnesium, and alloys thereof. By means of these chemical elements and compounds, more lithium can be reversibly stored than with graphitic carbon. Silicon anodes have a theoretical capacity of 3578 mAh/g at room temperature, for example. However, when these novel anode materials are used, a substantial volume change in the anode of as much as 300 to 400 volume percent occurs during the lithiation and delithiation due to the specific lithium storage mechanism (conversion reaction). The surface layer, also referred to as SEI (Solid Electrolyte Interface), that forms on the anode surface during the initial cycles is mechanically and/or chemically damaged because of the volume change in the anode during repeated lithiation and delithiation, however, and must be formed again for this reason. This results in a continual loss in capacity of the lithium-ion battery, among other effects.